1. Field of the Invention
This invention relates in general to an apparatus for setting a cement plug in a well, and in particular to an apparatus lowered through tubing on wireline for forming the plug.
2. Description of the Prior Art
In an oil and gas wells, there are occasions when it is desired to set a plug in the casing above perforations to seal off the formation surrounding the perforations. This can be done by lowering a bridge plug on tubing or wireline. However, such procedure requires pulling the tubing out of the well if tubing is already in place. This procedure is time consuming, expensive, and may not be necessary.
Wireline devices are in use that are capable of being lowered through tubing and setting a cement plug below the tubing in the casing. In this procedure, a retainer is first lowered and set. The retainer is a collapsible metal device that has dogs that spring out to grip the casing wall. A fan shaped basket spreads out to retain cement dropped on the retainer. Then, a dump bailer is lowered through the tubing. When in position above the retainer, the dump bailer is actuated to dump cement onto the retainer. Often, several runs will be necessary to dump several feet of cement onto the retainer.
The dump bailers are of various types. In some, it is difficult to refill the bailer with cement as some require loading the cement slurry from the top. The tool is often 30 feet long, and normally has to be lowered into and pulled from the well through a pressure lubricator mounted to the top of the well. If top filling is required, the pressure lubricator may have to be removed and laid down for each run. Also, some dump bailers lack a positive means to push this cement out from the tool, relying only on gravity. This results in stringing the cement out through the well.